It is commonly known that, much like Pavlov's dogs salivating in response to hearing the bell they associate with dinner time, smokers feel cravings and have physiological reactions to pictures they associate with smoking.

Activation of two different kinds of neurons is necessary for appetitive and aversive memory recall in crickets. Researchers writing in the open access journal BMC Biology blocked octopaminergic (OA-ergic) and dopaminergic (DA-ergic) transmission and found that this resulted in the inability to recall pleasant and unpleasant memories, respectively.

Fear is a powerful emotion and neuroscientists have for the first time located the neurons responsible for fear conditioning in the mammalian brain. Fear conditioning is a form of Pavlovian, or associative, learning and is considered to be a model system for understanding human phobias, post-traumatic stress disorder and other anxiety disorders.